The machine vision industry commonly employs laser beam projection systems for precision alignment and for determining the three dimensional shape of objects. A pattern of laser lines is projected onto the object and the resulting beam deflections are used to determine the surface profile. A laser beam can easily be expanded into a line by attaching a cylindrical lens onto the front of the laser, however, expanding a typically gaussian laser beam into a series of lines results in a gaussian intensity distribution along the projected lines. This results in thresholding problems for the silicon detectors commonly used.
U.S. Pat. No. 4,826,299 to Powell describes a single optical element which projects a uniform intensity laser line, and this, in combination with a diffraction grating can be used to project a grid of such lines.
While the Powell element is useful, in order to obtain more information about the object under test it is preferable to project the laser beams in at least two intersecting directions. For these applications, and also for precision alignment purposes, a laser cross is desirable. Methods commonly used to achieve a cross-shaped beam distribution include using lenses to image the laser beam onto a mask, thus throwing away much of the light. These systems, however, are complex and also suffer from non-uniformity along the length of the projected lines.